The design of the two smartwatches are very different.
The Gear S has a single button under a curved 2-inch screen, while the strap is just as wide as the face of the watch. The big screen and wide strap gives it a larger-than-usual appearance for a watch.
The Apple Watch has a more intricate design as the company appears to have focused more on the fashion aspect of a wearable device.
The Digital Crown on the side of the 42mm face of the watch makes it seem more like your everyday watch.